Resistance unit



Feb. 12, 1929. 1,702,062 0. SONKIN RESISTANCE UNIT Filed Oct. 23. 1920 2 Shaets-Sheet l INVENTOR DAVID .soumu ORNEY Feb. 12, 1929.-

n. SONKIN RESISTANCE UNIT Filed Oct. 23, 1920 2 Sheets-Sheet 2 IINVENTOR DAV SONKIN BY TTORNEY Mata 12.1929.

navm norm. 01

NEW YORK, N. Y.,

ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION 01 DELAWARE.

RESISTANCE UNIT.

Application filed October as, 1920. Serial No. 418,958.

This invention relates to resistance units, and more especially to a high resistance element particularly suitable for use in a unit forresistance type amplifiers, or as a grid leak for radio vacuum tubes in various forms of vacuum tube apparatus, although the invention is not limlted to these uses and may be employed in any apparatus inwhich it is found suitable.

The primary object of the invention is to secure a high resistance, of the order of two megohms for instance, which is small and compact, simple in construction, of low cost, and reliable and stable in operation whether in radio work or line telegraphy, telephony,

' or land or submarine cables.

Illustrative examples of various preferred forms of the resistance element and resistance unit are shown in the accompanying drawings, in which,

Fig. 1 is a face view of a portion of a large .strip or piece of prepared resistance material before cutting;

Fig. 2 is an enlarged face view of a small resistance strip or element before attachment of the contacts;

Fig. 3 is a side view partly in section and partly broken away showing the method of attaching contacts to the element in the form of eyelet pieces means of a punch or tool;

Fig. 4 is an enlarged detail longitudinal sectional view of an eyelet piece before clam ping;

Fig. 5 is a detail top plan view of an eyelet piece with-connector or leading-in wire engaging the same;

Fig. 6 is a detail elevation of Fig. 5;

Fig. 7 is an enlar ed detail sectional elevation of a portion 0 a resistance element and an eyelet partly broken away and clamped to the element, this view being taken on line 7,7 of Fig. 8;

Fig. 8 is a plan View of a resistance strip or element after the attachment of the cont-acts;

Fig. 9 is an enlarged longitudinal sectional view of a complete resistance unit containing a resistance strip or element;

Fig. 10 is a full size side elevation of a modified form of resistance unit in a mounting, which is also adapted to receive and hold th form of unit shown in Fig. 9;

' Fig. l t is a detail perspective view of a plug and contact for the unit shown in Figs. 11 and 12; and

Fig. 15 is an enlarged side view, partly broken away and partly in longitudinal section showing a modification of Fig. 12.

By way of example, my invention will be described in detail with reference to a. preferred form of high resistance unit in accordance with the invention. As shown in the drawings, this comprises a capsule or cartridge type of device having a high resistance strip or element within a tubular container, preferably of suitable insulating material such as glass, and terminal caps are provided at the ends of the container. The completed unit is adapted to be removably held in convenient manner in a spring mounting as shown of actual size in Fig. 10. Any desired number of such resistance units may be mounted side by side or in any other suitable arrangement and connected in circuit as'desired.

Among'the important features of the invention are the composition of the resistance film to be placed upon a strip of material and the method of preparing the resistance strip orelement.

A liquid composition of the nature of carbon, such as lamp-black, fine graphite or high calcined petroleum coke suspended in glue, gum, gelatine, or glutinous vegetable juices and the like, or in general, a mixture of finely divided carbon and a liquid of suitable consistency to hold the carbon in sus ension, is a suitable composition forthe resistance film. I have found that waterproof india ink for drawing purposes satisfactorily fulfills the requirements of my invention and is a ready and convenient source of supply of such prepared material. The india ink may be used alone or in combination with finely divided graphite such as is commercially known as grade H graphite, a'suitable proportion being six parts of india ink to one part of graphite thoroughly mixed together. The

absorbed by the sub-surface fi res, and when dry produces a satisfactor film. Of the various thicknesses'of bristo board obtainable,

sible.

even film is obtained.

three ply quality is found most satisfactory for my purposes.

. In preparing the film, a large strip or sheet of bristol board, which may conveniently be about eight to ten inches long and about two inches wide, a portion of which is indicated in Fig. 1 at A, is coated preferably on both sides with the mixture of india ink and aphite dust, for example, in the followmg manner: The two inch strip A is tacked down or otherwise held upon a plane surface, and a moderate amount of india ink solution istaken upon a linch flat varnish brush, preferably a camels hair brush, of good quality, so that hair marks are not left on the surface. A sin 1e, firm, longitudinal stroke is made the entire length of the strip A. This is followed by a series of transverse strokes, always beginmng from the same edge and lapping each stroke over the previous one a little. A second lengthwise stroke is then taken, which is also followed by a series of transverse strokes as before. In this manner eve portion of the paper is traversed at least our times and b this! procedure an The only time that the brush is dipped is previous to the initial stroke. When the surface has dried the strip is turned over, and the same procedure repeated on the other side. In the com lete process, four coats .have been provide on each side. The strip when dry has an even surface along its entire length save for quarter inch belts B on the outside edges indicated in approximate extent by the dotted lines a. The main belt between-the dotted lines a is usable for resistance, whereas the portions B are-'not suitablefor this purpose. The size and dimensions of the original strip A, the number of coats applied and the met 0d of application may be varied according to the results desired. In any case the object sought is to produce a thin conductive film which is as uniform and even as pos- The film applied to each side in the manner described as a thickness of approximatelg eone to two thousandths of an inch and may varied over a. wide range. However,

for practical reasons it is undesirable to have a film of greater thickness than of the order ably be about 5/16 inches wide, an each strip has a usable film about-1-1/2 "inches Ilong with imperfect end ortions about 1/4 inch long as indicated in j ig. 2. 4

The small resistance strips orelements are now ready for the attachment of suitable contacts and incorporation in acomplete resistance unit. One practical and simple means of making an efiicient contact to the film is by using eyelets, and I have found that the eyelet known as the solidhead eyelet,v is a satisfactory device which does not darn-, age the film. This is important, because damage to the film may raise the resistance. These solidhead eyelets D shown in the figures are made of special material and are fastened in place by a pair of pliers (shown at E, Fig. 3) which forms them so that curved and rounded surfaces F and G bear upon the coated paper as shown in Fig. 7. A1l-cracking of the film is avoided by this means, and good contact to the film is made.

It is difficult to estimate the exact-number of coats of ink solution and the size of strip or element necessary to give a definite required resistance, but by variations of the length or width of the strips, or the number of coats or composition of the coating material, variations may be secured over considerable range. I have found that for a resistance of two megohms for instance, a film consisting of four coats per side of the composition set forth, on strips of the size'hereinefore stated is about correct. However, the safest way is to measure the resistance .between eyelet contacts ofa sample strip, and if the resistance is too low, the long edges of the strip may be trimmed down, or a sample may be made up with slightly greater distance between the centers of the eyelets. Having obtained a sample of the required resistance element, the remainder of the piece of bristol board A may be cut up and. resistance elements made in accordance with the sample in uantity production, each' one being prefera ly tested. In every'case the distance between the outer rim of the e elet D and the long edge of the strip 0 shou (1 referably be at least 3/64 of an inch in or er to avoid breaking the paper at the eyelet.

In clamping the eyelets D to the strip C, a hole H is punched in the strip for example, about 1/2 inch in from the end of the strip, and the strip is left on the stud' J of the liers E as shown in Fig. 3. The eyelet D isp aced i of the eyelet D is curled and clamped around over the stud J, anda bare stranded copper wire K, which may consist of four strands of #30 B. & S. gage, is wound around the eyelet as shown in detail in Figs. 5 and 6, leaving the long free end L for the connector or leading-in wire. The eyelet D is then clamped with a firm pressure, but not violently, in order to avoid breaking the bristol board, until the eyelet is flattened into the form shown in enlarged sectional detail view in Fig. 7 As there indicated, the material and in contact with the wire connector K. A second eyelet D with its connector K, is clamped the desired distance, about 5/8 of an inch center to center, away from the first eyelet on the strip C, and the superfluous paper is then cut off substantially at the dotted lines a, leaving a unit about one inch in length. The strip with the eyelets in place is s own in Fig. 8. I

The advantage of the method described of attaching the connectors or leading-in wires K to the eyelets, resides in the fact that soldering the wires directly to the eyelets is avoided, because soldering results in damage by heating, to the resistancefilm in the neighborhood of the eyelet.

It is to be noted in connection with Fig. 7 that there is an absence of any break in the film surface, which is an advantage of this particular type of contact; the contact between the film, leading-in wire K and eyelet D is positive and over the entire available surface; and the film of ink solution appears upon the surface of the bristol board at the crimped portions.

The complete resistance strip or element constructed as described is now ready to be put into a container as shown in Fig. 9, which may consist of glass tubing 0 out to the proper length for a unit of the desired size. Cork plugs .P are preferably put over the connectors or leading-in wires K of the resistance strip and these plugs P are inserted in the ends of the tube 0, and preferably trimmed ofl close to the glass, care being taken not to nick or scratch the leading-wires K of the resistance stri and these plugs P are inserted in the ends 0 the tube 0, and preferably trimmed off close to the glass, care being taken not to nick or scratch the leadingin wires. 1

Cap terminals Q, preferably made of cop er or brass of the desired thickness and pre erabl nickel plates are then laced over the end of the tube 0 and are eld in position with a suitable sealing compound, as for instance, plaster of Paris R as indicated in Fi 9. To prevent moisture of plaster of Paris from entering the tube 0 the ends of the cork plugs P are preferably painted with beeswax before putting on the caps Q. To prevent the beeswax from melting when the ead-in wires K are soldered to the caps at S,

the soldering is preferably done before and not after sealing; that is, the cap Q is soldered onto the leadin -in wire K a suitable distance, about inch fromthe cork plug P, beeswax is spread over the ends of the plugs, plaster of Paris is put into the caps, and the caps and leads are sealed in place over the ends of the tube O.

The resulting product is a reliable unit resistance of compact and stable form. The resistance film on the strip or element C in some respects acts as a carbon compression, because if one side only of the paper strip is coated, I have found that the resistance decreases when the paper is bent so' that the film articles are compressed and the resistance increased when the particles are put under tension. -This occurrence makes it highly desirable to coat both sides of the paper, in order that bending of the stri when it is placed in the glass container 0 s all not produce considerable variation.

Figs. 11 to 14 inclusive illustrate a modification of'a resistance unit in which a different form of contact for the resistance strip or element is employed. In this modification, strips T of thin copper are carefully wrapped around the ends of the resistance strips C andclamped tightly to the strip to obtain good contact. Care should be taken that the edges of the contact strips T do not cut into the thin resistance film, which might disturb its continuity and considerably increase the previously measured value of resistance.

One way of balancing for this loss is to lead pencil the ends of the resistance strip prior to attaching the metallic contacts T and make connection on the penciled parts. Furthermore, after the contacts T are in place at each end and the resistance measured, if the resistance is too high, it may be reduced by adding a small pencil mark shown at U in Figs. 11 and 12 on the coated paper, in order to adjust the resistance of the element to the proper value of two megohms or such other value as desired.

In assembling the resistance unit shown in Figs. 11 to'14, the connectors or leading-in wires Kare first soldered at V (Fig. 13) to the clips or contacts T, and the clips are clamped to the ends of the coated bristol board resistance strip C. One cork plug P is suitably pierced and slipped over the end L of one connector or leading-in wire K, and this assembly is inserted in the glass tube C, the other plug P is then pierced and slipped over wire L at the other end and brought down into the end of the tube 0. The wires L are bent back around the ends of the tube as shown and the cap terminals Q, are sealed in place over the ends of the tube, in this instance by sealing wax W if desired. In Fig. 15 another modification is shown substantially similar to that described in connection with Figs. 11, to let, except that the cap terminals Q are filled with melted Woods metal X and are thus held in position on the ends of the tube O. In this case contact'is' made between the wires L and the cap terminals Q, through the conducting agency of the Woods metal.

' The form of mounting shown in Fig. 10 is suitable for an of the forms of reslstance units illustrated and described. It consists of an insulating base Y 'havin spring contact arms Z spaced the desired istanoe apart and held in position by the screws d. Screw binding osts e carried by small brackets f are suita ly mounted at the bases of the arms Z and held in position by the screws d. The insulating base Y is also preferabl provided with socket holes 9 to receive suita le fastening devices for securing the mounting to a support.

claim and desire to obtain by Letters Patent the following:

I 1. A grid leak for vacuum tubes consisting of a container of insulating material, a high resistance element within said container, contacts carried by said element, insulating plugs for said container, connectors for said contacts extending through said plugs and metallic cap terminals secured over the ends of said container in contact with said connectors.

2. A grid leak for vacuum tubes consisting of a container, a resistance element within the container, comprising a strip of non-absorbent insulating material, a film of carbon upon the surface 'of said paper, means for sealing the ends of said container, metallic cap terminals for the ends of said container and connectors electrically connecting the resistance element with the said cap terminals.

3. A grid leak for vacuum tubes consisting of a container, a resistance element within the container, comprising a strip of non-absorbent insulating material, a film upon said surface formed from a liquid coniposition of finely divided suspended carbonaceous material, metallic cap terminals sealed over the ends of said container and connectors electrically connecting the resistance element with the said cap terminals.

4. A grid leak-for vacuum tubes consisting of a container, a resistance element within the container, comprising a strip of non-absorbent paper, a film upon the surface of said strip formed from india ink, metallic cap terminals sealed over the ends of said container, and connectors electrically connecting the resistance element with the said cap terminals.

5. A resistance element comprising a sup port of insulating material having a thin adherent film of conductive material thereon, and a terminal in the form of a hollow rivet extending through the support and film fior establishing electrical contact with the 6. A high resistance element comprising a support 0 insulating material having a thin adherent film of conducting carbonaceous material thereon and a hollow rivet extcndin throughsaid support and film for establis in electrical contact with the film.

7. hi h resistance element comprisin a support 0 insulatin material havin at in adherent film of conducting material iliereon, a hollow rivet extendin through said support and film, and a con uctor coiled around said rivet, said rivet being'compressed to establish intimate contact between said conductor and film.

8. A grid leak-comprising a high resistance element, an insulated container for said element, means within said container for supporting said element at spaced intervals in said container, conductors extending through said supporting means, and fusible metal tips over the ends of said container contacting with said conductors.

- 9. A grid leak comprising a high resistance element, an insulated open-ended container for said element, cork plugs in the ends of said container adapted to support said element, and conductive terminals over the ends of said container.

10 A high resistance element for electrical circuits comprising a su port of hard-surfaced and highly polis ed non-absorbent paper and a dry film of a glutinous carbon containing substance coating the surface thereof.

11. A process of preparing a high resistance element which consists in applying a coating of uniform thickness of a glutinous carbon containing fiuid to a hard-surfaced highly polished non-absorbent paper, and drying the coating to produce an adherent high resistance conducting film of carbon contaming material on the surface of said paper.

12. A grid leak comprising a high resistance element, an insulated container for. said element, means within said container for supporting said element at spaced intervals in said container, end caps over the ends of said container, and low fusible material between the ends of said container and said caps, said low fusible material being adapted to secure said element in position and to seal the ends of said container.

13. A grid leak comprising a high resistance element, an insulated container for said element, means at the ends of said container for supporting said element at spaced intervals from the walls of said container by means of conducting member extending from the ends of said resistance element and through said supporting means, a cap over each end of said container, and low fusible material between'the ends of said container and element support and said cap, said material being adapted to seal the ends of said container and to provide a contact surface for said pro'ecting conducting members.

14. A gri leak'comprising a high resistance element, an insulated open-ended conof said container, and a low fusible material tainer for said element, cork plugs mounted between the ends of said container and said in the ends of said container,-conducting cap, said material being adapted to seal, the 10 members extending from the ends of said ends of said container and to provide contact resistance element and projecting through between said projecting conducting members and beyond said cork plugs in the ends of and said cap.

said container, a conducting cap at each end DAVID SONKIN. 

